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+86 13143444311
Email：sst@szsst88.com
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Address：Building 9, First Industrial Zone, Tantou Industrial City, Songgang Street, Baoan District, Shenzhen 518105, Guangdong, China
Type:Hex Socket Flat Head Cap Screw, M4 Countersunk Machine Screws
Materials:Stainless Steel
Surface treatment:Plain
Head Type:Flat (countersunk)
Drive:Hexagon socket (Allen)
Thread:Machine thread
Point:Plain, chamfered
Forming:Single Die Heading
Size:M1 M2 M3 M4 M5 M6 M7 M8 M9 M10
We make hex socket flat head cap screws in stainless steel, quoting them from M1 to M10 with lengths made to the drawing. The head series and countersink angle are agreed on the drawing, and the first article is seated in your own machined plate.
Watch the factory video·Email sst@szsst88.com
ISO 9001:2015 · Manufacturing since 1998 · 8,678+ customers · 89 countries and regions
Made to order – there is no stock catalogue. Each part is produced to your drawing, and production starts after drawing review and first-article approval.
Hex socket flat head cap screws are countersunk screws with a hexagonal socket, so the head sits flush in a cone and is driven from inside. The part recorded here is stainless steel, plain finish, quoted from M1 to M10 with lengths made to the drawing.
Flat head. A conical underside at 90 degrees that seats in a countersink so the top finishes level with the surface.
Hexagon socket. An internal hexagon driven with an Allen key, sitting inside the small flat on top of the cone.
Stainless body. The alloy carries the corrosion resistance; there is no coating to change the seat.
Machine thread. A uniform thread for a tapped hole, a nut or an insert.
They are used where a fixing must not stand proud: machine beds, sliding surfaces, mould platens, covers that pass under a seal, and any joint where a bolt head would be a snag or a trap for debris.
A countersunk head spends its height on the cone. A cap head of the same thread can be tall because its height is solid metal; a flat head has to bury most of itself in the countersink, so what remains above the cone is a thin disc with a socket cut into it. That is the first constraint on this part and everything else follows from it.
The socket therefore cannot be as deep as on a cap head. It has to be shallow enough to leave a floor of material under it, and that floor is what carries the drive load into the cone. A shallow socket means a shorter key engagement, which means the drive is the limit long before the thread is, and the limit gets tighter as the size goes down.
The second constraint is the standard. Countersunk socket head screws exist in more than one head-height series, and the heights do not match at every size. A part made to one series will seat in a countersink cut for the other, but its top will sit a little high or a little low, and on a surface that has to be flush that difference is the whole problem.
That is why a replacement needs the series, not just the thread and length. Two screws that both pass an M4 check, both have a 90 degree cone and both take a 2.5 mm key can differ in head height by an amount you can feel with a fingernail, and a machine bed with sixty of them will show the difference as a pattern.
At M4 the three dimensions squeeze each other tightest. The cone needs its depth, the socket needs its floor, and the head has little height to divide between them. A part that is made slightly low in head height looks cleaner and drives worse; a part made slightly high seats less and stands proud.
The recorded range is M1 to M10, with lengths made to the drawing. Custom lengths up to 2,000 mm are subject to the drawing submission and DFM review. The quotation for hex socket flat head cap screws carries the head diameter, the countersink angle, the head height, the socket size and depth, the thread pitch and the overall length measured over the head.
| Item | How it is defined | What we control |
|---|---|---|
| Cone | Countersink angle, usually 90 degrees | Angle and concentricity |
| Head diameter | Widest point of the cone | Diameter and edge sharpness |
| Head height | Top face to the cone top | Height to the series named |
| Socket | Hexagon, key size per diameter | Depth and floor thickness |
| Thread | Machine thread in stainless | Pitch, length and start position |
| Length | Overall, head included | Length tolerance and thread start |
Head height and socket depth are measured as a pair, because they come out of the same forming stroke and the same broaching depth. A head that is pressed a little low leaves less material above the cone, and the socket cut to its nominal depth then has a floor that is too thin.
The countersink angle belongs on the mating part’s drawing as well as on the screw’s. Ninety degrees is the common metric practice; 82 degrees appears on older drawings, and a 90 degree head in an 82 degree seat bears on the rim and stands proud no matter how hard it is driven.
Length is measured over the head, so the datum agrees with the countersink. In a joint where the head sits in a machined seat, the effective thread length is the overall length minus the cone depth, and that is what decides engagement.
Four properties decide hex socket flat head cap screws, and each one carries a cost:
| Property | What it gives | What it costs |
|---|---|---|
| Flush head | Nothing stands above the surface | Head height is spent on the cone |
| Socket drive | Torque without a slot or cross | Shallow socket at small sizes |
| Cone seat | Load spread over a wide cone | Needs a matching counterangle |
| Stainless body | Corrosion without a coating | Lower strength than a graded steel part |
The value is a surface with no obstructions. Where a part slides, seals or is cleaned, a fixing that stands proud is a defect, and a flush socket head is the only form that gives high drive torque without a protruding head.
The cost is depth. The socket has to be shallow, the key has a shorter engagement, and the head has no material to give if the countersink is not cut to match. A flush head is unforgiving in a way a pan head is not.
The recorded finish is plain over stainless. The alloy carries the corrosion resistance and the cone needs no coating, which matters because the cone is the load-bearing surface and a plated layer there changes both the fit and the friction of seating.
| Option | How it protects | Effect on cone and socket | Typical use |
|---|---|---|---|
| Passivated, plain | Removes free iron; rebuilds oxide | No build; cone as cut | Default for stainless |
| Electropolished | Levels the surface | Cone edges rounded slightly | Food, medical, cleanroom |
| Black oxide on stainless | Colours the surface | Thin film; seat unchanged | Dark machine beds |
| Nickel plated | Hard bright barrier | Build on the cone; seating changes | Where a bright seat is wanted |
| Zinc plated steel equivalent | Sacrificial zinc | Build on cone; friction changes | Where stainless is not needed |
Passivation reaches the cone as well as the socket, and both are checked. Free iron collects in the cut features, and a flush head that rusts at its cone shows a ring inside the countersink that cannot be cleaned out once the screw is seated.
Where a plated version is used, the cone is gauged after plating. A film on the cone changes how the head beds in: it seats a fraction higher, develops friction differently, and on a flush joint that can mean a visible high spot.
Three settings where the surface has to stay clear:
| Where it sits | The screw fixes a plate where the surface is machined flat and must stay flat for a workpiece or a mould. |
| When it goes wrong | Heads that are not flush leave witness marks on the workpiece, or stand proud of the bed. |
| Why it happens | The surface is machined, the fixings are numerous, and flatness is inspected. |
| What we control | Head height and cone angle checked; first article fitted in the machined seat. |
| Where it sits | The screw holds a strip where a scraper, a seal or a slide passes over the joint. |
| When it goes wrong | A proud head wears the seal or the scraper and the joint begins to leak. |
| Why it happens | The joint moves, the surface is finished, and the fixing is covered. |
| What we control | Head height measured to the series; first article assembled and cycled. |
| Where it sits | The screw closes a cover on equipment that is washed, where debris would collect around a raised head. |
| When it goes wrong | Material packs into the hexagon and cannot be cleaned out, or a head corrodes in the pocket. |
| Why it happens | The joint is exposed, hygiene is audited, and the fixing is removed for cleaning. |
| What we control | Passivation verified on the socket and cone; first article cleaned and inspected. |
Four reasons that matter on a flush head at small sizes, each tied to something the drawing has to prove:
|
Head series and cone angle named
The head height series and the countersink angle are agreed before quoting, because two flush heads of the same thread can sit at different heights in the same seat. Basis: Series and angle on the drawing. |
Headed, broached, threaded, passivated
The cone and the top face are formed in one stroke, the socket broached to a controlled floor, the thread rolled and the batch passivated. Basis: One route from wire to flush part. |
|
Height and socket measured together
Head height and socket depth are measured as a pair and the key engagement proved, because a shallow socket is the failure that looks like a good part. Basis: Height and socket as one pair. |
Same height across orders
The heading punch and the broaching depth are recorded with the drawing revision, so a repeat order sits in the same seat at the same height. Basis: Same flush height across orders. |
These screws are headed on single-die machines that form the cone and the flat top in one stroke, broached with a hexagonal punch, thread rolled on the stainless shank and passivated as a batch. The first part of every run is measured on head diameter, cone angle, head height, socket size and depth, thread and length.
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Forming the cone while leaving enough height for the socket is the balance in this part. The metal flows from the shank out into the cone and up into the small disc on top, and a punch that is pressed a little too far produces a cone that is correct and a top that is too thin. Both measurements are taken on the first article because each one alone looks acceptable.
Broaching the hexagon into that thin disc is the operation that limits the part. The punch displaces material downwards and sideways, and there is little room for it to go; a punch set a few hundredths too deep leaves a floor that yields at the first drive, and a punch set shallow leaves a socket that will not take the key far enough to reach the torque the thread could carry.
Passivation comes last and has to reach into the socket and across the cone. Both are cut features with internal corners that hold contamination, and on a flush head those are the two surfaces nobody can inspect once the part is installed.
What decides whether hex socket flat head cap screws pass is the head height, the cone, the socket and the thread. The inspection agreement covers those, and the criteria come from the drawing.
Height and cone on the projector |
Thread and start checked |
Hardness against the stainless spec |
Salt-spray testing of cone and socket |
Head height is measured from the top face to the top of the cone, not across the whole part, because that is the dimension that decides whether the head finishes flush. The cone angle and head diameter are measured on the same setup, and the socket depth is read against the head height to confirm the floor.
The socket is proved by driving with the production key at the torque the joint calls for and inspecting the floor and the walls under magnification. On a flush head the floor is the thin feature, and a floor that has begun to dish is a part that will fail on the next service rather than on this one.
A sample from every batch is seated in a countersunk test plate of the agreed angle and checked for rocking and for proudness. That is the check that catches a head height mismatch, and it is recorded with the batch.
Every batch is traceable to the heat of stainless it was made from. The grade and heat number appear on the material certificate supplied with the parts, and the inspection records follow the criteria agreed on the drawing.
ISO 9001:2015 |
RoHS test report |
Registered trademark |
Patent: security screw and driver |
With each shipment we supply the material certificate, the inspection record for the dimensions on the drawing including the head height and cone angle, and the passivation records for the batch. The documents carry the drawing revision and the batch number, so a repeat order of hex socket flat head cap screws sits at the same height.
More than 8,678 customers in 89 countries and regions have ordered from Shi Shi Tong; 87% of orders come from repeat customers and 56% through referrals. Most projects follow the same route: drawing review, first-article approval, then batches checked against that sample. On a flush head the first article is seated in the customer’s machined plate, because proudness only shows against the real seat. Buyers visit during the process to review samples.
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8,678+
customers served
|
87%
of orders from repeat customers
|
56%
of orders through referrals
|
89
countries and regions shipped to
|
Buyers and quality engineers visit for sample review, process discussion and supplier audits; the visit is arranged around production so the headers and the broaching station can be seen on the day the parts run.
Customer group visit – sample review |
Customer group visit – process discussion |
Customer group visit – factory tour |
Customer visit – project kick-off |
Danish customer – drawing review |
Industry exhibition – meeting customers |
The cone uses most of the head height, so the socket has to be cut into a thin disc with a floor left under it.
They are made to different head-height series. Both seat in a 90 degree countersink, but the top face lands at a different level.
Yes. A 90 degree head in an 82 degree seat bears on the rim, rocks and stands proud however hard it is driven.
That is what it is for: nothing stands above the surface, so a seal, scraper or slide passes over it.
The socket and the floor under it, not the thread. At small sizes this is the tightest constraint on the part.
Head diameter, countersink angle, head height and its series, socket size and depth, thread pitch and overall length.
How a flush head socket screw project runs from drawing to repeat delivery:
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1
Send the drawing and the countersink angle
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→ |
2
Head series and socket depth agreed
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→ |
3
First article seated in your plate
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→ |
4
Batch production and repeat orders
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Each step is confirmed with you before the next one starts; the drawing revision from the first article is what repeat orders are checked against.
For a quotation, send the drawing with the head diameter, countersink angle, head height, socket size and depth, thread pitch and overall length.
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Head diameter
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Cone angle
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Head height
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Socket size
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Thread pitch
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Length
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Sending a drawing? The form below does not take attachments. Email the PDF, DXF or STEP file to sst@szsst88.com with the part name and quantity in the subject line – the drawing is reviewed and a quotation follows.
+86 13143444311
sst@szsst88.com
